1. Field of the Invention
This invention relates to a tap device, and more particularly, to a tap device for use in broadband communications systems having a receptacle area electrically positioned between and connected to an RF signal coupling element and an RF signal splitting element for receiving a plug-in intermediate circuit having a preselected electrical configuration to provide a tap device capable of being utilized in a variety of applications.
2. Description of the Prior Art
It is well-known in the communications industry to provide a tap device for attenuating RF signals provided from a source for delivery to a plurality of loads or subscribers connected to the tap device outlet. Tap devices normally provide a fixed degree of attenuation of a source RF signal so that the load or subscriber connected to the tap device outlet can use the attenuated RF signal for any particular application. The degree of attenuation of the RF signal passing through the tap device is dependent upon the hardwired tap device electrical circuitry. Tap devices normally include a base housing having means for securing a coaxial cable connected to the tap device. The tap device also includes a cover plate having an inner surface upon which is mounted the tap device electrical circuitry for providing a preselected degree of attenuation of the RF signal delivered from the source, and a plurality of outlet taps mounted on the cover plate outer surface for connection to a plurality of loads or subscribers.
Although tap devices for broadband communication systems are known, a problem inherent with the prior art tap devices is that, since the electrical attenuation circuitry consists of fixed electrical components which are hardwired on the tap device cover plate, if it is desired to change the attenuation value of the tap device, the cover plate must be removed and a new cover plate installed which includes circuitry having a different preselected attenuation value.
U.S. Pat. No. 3,881,160 discloses a multi-tap distribution box for a CATV system, the box being interposed in a primary line carrying radio and video signals from a master station to subscribers who are linked to the primary line by secondary lines coupled to the taps on the box. The box consists of an open housing having input and output parts interconnected through a normally closed switch whereby signals pass through the housing. Removably secured to the housing is a tap cover plate having a distribution network mounted on its inner face, the network being connected to a group of taps projecting from the outer face. The plate further includes means to engage and break open the switch whereby the distribution network is rendered inoperative to supply the signals to the taps.
U.S. Pat. No. 3,895,318 discloses a multi-tap distribution box for a cable television system, the box being interposed in a distribution line carrying audio, video, or other electrical signals or data as well as power to and from subscribers who are interconnected to the distribution line by means of secondary lines coupled to taps on the distribution box. The box consists of a housing having input and output ports, and a tap cover plate having a distribution network mounted on its inner face. The network is connected to a group of taps projecting from the outer face, means being provided to connect the network to the input and output ports when the tap plate is in place and to disconnect the network from the ports when the tap cover plate is removed from the housing.
Although the prior art tap devices described herein all provide means for attenuating an RF signal provided from a source and means for delivering the attenuated RF signal to a plurality of subscribers, these prior art devices are limited in that they are composed of electrical components which are hardwired to the tap box cover plate assembly. As a result, if it is desired to change the attenuation value of the tap device for any reason, the tap cover plate must be removed and a new cover plate installed having the proper electrical circuitry to provide the desired degree of attenuation.
As seen, maintaining an adequate inventory of tap cover plates each having a different preselected attenuation value is a major logistics concern for both the user and the supplier of the tap units. Tap cover plates must be maintained in inventory not only for each preselected degree of attenuation desired, but also for each preselected number of output taps required. For example, it may be desired to maintain a tap cover plate inventory for use in single-cable split-band broadband communications systems to accommodate known-in-the-art subfrequency split, mid frequency split and high frequency split filtering and attenuation circuitry. It also may be desired to maintain a tap cover plate inventory for dual cable systems in which the tap cover plates have attenuation values in 1 decibel increments ranging from 4 to 40 decibels. If individual hardwired tap cover plates were to be maintained in inventory to cover all possible single-cable split-band sub, mid and high frequency configurations and all possible dual dable attenuation configuration, the total number of individual hardwired tap cover plates required to be maintained in inventory would number in the thousands.
Therefore, there is a need for an improved tap device which includes the basic tap device circuitry mounted on a tap cover plate and also includes receptacle means electrically positioned on the cover plate between the tap device RF signal coupling element and the tap device signal splitting element. A portion of the receptacle means is electrically connected to the RF signal coupling element and a portion of the receptacle means is connected to the RF signal splitting element. The receptacle means is designed to accept a plug-in intermediate circuit which, when inserted into the receptacle means, provides an electrical connection between the RF signal coupling element and the RF signal splitting element. The plug-in intermediate circuit may either be a short circuit feedthrough, in which case, the tap device can operate as a standard CATV tap unit, or an attenuator which can be plugged into the receptacle means to provide a further, finer degree of attenuation of the RF signal passed through the RF signal coupling element. The intermediate circuit may also include a combination of duplex filters and plug-in attenuators to convert the tap device from a standard CATV tap device to a tap device usable for single-cable split-band communications systems.